The present invention is directed to hydraulic regeneration. More particularly, the present invention is directed to a system and method for accumulating and using regenerated hydraulic energy.
Work machines are commonly used to move heavy loads, such as earth, construction material, and/or debris. These work machines, which may be, for example, wheel loaders, excavators, bulldozers, backhoes, and track loaders, typically include at least two types of power systems, a propulsion system and a work implement system. The propulsion system may be used, for example, to move the work machine around or between work sites and the work implement system may be used, for example, to move a work implement through a work cycle at a job site.
The efficiency of a work machine may be measured by comparing the amount of energy input into the work machine with the amount of work performed by the work machine. Typically, a work machine will include an engine that powers both the propulsion system and the work implement system. Thus, the energy input to the work machine may be measured as a function of the amount of fuel supplied to the engine. The work output of the work machine may be measured as a function of the work performed by the propulsion system and the work implement system. A work machine with a high efficiency will perform a greater amount of work on a given quantity of fuel.
A work implement system for a work machine may include a hydraulic system that is powered by pressurized fluid. In this type of system, a source of pressurized fluid converts energy generated by the combustion of fuel in the engine into pressurized fluid. This pressurized fluid may then be directed to a hydraulic actuator, which may be, for example, a hydraulic cylinder or a fluid motor, to move the work implement. Because the pressurized fluid represents energy, the efficiency of the work machine is reduced when pressurized fluid is released to a tank. The reduction in efficiency results from the release of energy as heat to the tank as the pressure of the fluid drops. In other words, the release of pressurized fluid to the tank results in energy being used to add heat to the fluid in the tank instead of being used to move the work implement.
An exemplary hydraulic system for a work machine that recovers or recycles fluid from a lifting cylinder is described in International Publication No. WO 00/00748 to Laars Bruun. As described therein however, an additional pump operated by the drive unit of the work machine is required to communicate fluid between an accumulator and the head end of the lifting cylinder. Depending upon the desired direction of movement of the lift cylinder, and the pressure difference between accumulator and cylinder, the drive unit supplies energy to, or receives energy from, the hydraulic circuit. Thus, an additional energy input is required to recycle the captured energy and the efficiency gains are, therefore, minimized.
Energy may also be wasted by the propulsion system of a work machine. For example, a significant amount of energy generated by the engine may be converted to kinetic energy of the work machine through a transmission on the work machine. This kinetic energy is typically dissipated as heat through the brakes when the ground speed of the work machine is reduced.
Thus, the efficiency of a work machine may be improved by limiting the amount of energy that is inefficiently used or wasted during the ordinary operation of the work machine. In addition, the efficiency of the work machine may be improved by capturing energy in a device such as an accumulator that would otherwise be wasted. The captured energy may then be used in a future operation of the work machine, thereby reducing the fuel demands of the engine.
The hydraulic regeneration system of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a hydraulic system that includes a first hydraulic actuator having a first chamber and a second chamber, a second hydraulic actuator having a third chamber and a fourth chamber, and a source of pressurized fluid. A first directional control valve is disposed between the source of pressurized fluid and the first chamber of the first hydraulic actuator and the third chamber of the second hydraulic actuator. A second directional control valve is disposed between the source of pressurized fluid and the second chamber of the first hydraulic actuator and the fourth chamber of the second hydraulic actuator.
In another aspect, the present invention is directed to a hydraulic system that includes an accumulator, a source of pressurized fluid, a first directional control valve, and a second directional control valve. A first fluid line connects the source of pressurized fluid with the first directional control valve and a second fluid line connects the source of pressurized fluid with the second directional control valve. A third directional control valve is configured to control the rate and direction of fluid flow between the accumulator and the first and second fluid lines.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.